DE 20 2005 021 715 U1 has disclosed an adjustable camshaft for the valve gear of an internal combustion engine having an outer shaft, on which first cams are arranged which are arranged fixedly with said outer shaft so as to rotate with it, and an inner shaft extending through the outer shaft, to which inner shaft second cams are connected fixedly so as to rotate with it. The second cams are mounted on the outer side on the outer shaft. If the inner shaft is rotated with respect to the outer shaft in terms of its phase position, the control position of the first cams is displaced with respect to the control position of the second cams. A cam adjusting device which can be activated by way of compressed oil is arranged on the camshaft in order to change the phase position of the inner shaft with respect to the phase position of the outer shaft.
Oil is conducted in the radial gap between the inner shaft and the outer shaft, which oil is fed to the gap at a positive pressure. In order to supply the plain bearing seat of the second cams on the outer side of the outer shaft with oil, the outer shaft has at least one oil duct in the region of the second cams, through which oil duct oil is conducted out of the gap into the region between the second cam and the outer shaft. Here, the oil duct is formed by pin openings in the outer shaft, through which pin openings a pin is guided for coupling the second cam to the inner shaft.
The oil can be introduced via a camshaft bearing into the gap between the inner and the outer shaft, there being a plurality of camshaft bearings for mounting the adjustable camshaft in the cylinder head. One exemplary embodiment of DE 20 2005 021 715 U1 discloses a camshaft bearing which is arranged so as to adjoin a cam adjusting device, by way of which the inner shaft can be rotated with respect to the outer shaft in terms of its phase position. It is known here that the oil is conducted into the gap via the camshaft bearing which adjoins the cam adjusting device, which results in the disadvantage, however, that the configuration of the camshaft bearing adjacently with respect to the cam adjusting device has to be of complicated construction, since only a limited amount of installation space is available. The arrangement which is shown therefore does not make it possible to supply the cam adjusting device with oil from the gap between the inner shaft and the outer shaft, and the oil supply has to be configured separately.
The oil supply of the gap between the inner shaft and the outer shaft can usually take place via an outer camshaft bearing which is arranged so as to adjoin the cam adjusting device and mounts the camshaft in the cylinder head. The cam adjusting device can therefore be supplied directly via the compressed oil which is fed in, at the same time the gap between the inner shaft and the outer shaft being fed with compressed oil. This disadvantageously results in a pressure loss in the case of every second cam which is connected to the inner shaft, since a considerable outflow of compressed oil has to be determined through the oil duct into the region between the outer side of the outer shaft and the second cam. As a consequence, the oil supply of individual adjusting cams becomes less satisfactory as the distance increases from the infeed point of the oil via the camshaft bearing which adjoins the cam adjusting device. As a further consequence, the oil has to be fed into the gap between the inner shaft and the outer shaft at a plurality of locations.
If the oil is fed in via a camshaft bearing which is at a distance from the cam adjusting device, a pressure loss results over the axial course of the gap at every adjusting cam, with the result that the cam adjusting device is no longer supplied sufficiently with compressed oil from the gap between the inner shaft and the outer shaft.